1. Field of the Invention
The present invention relates to an image forming device, for example, a copying machine for duplicating an image of an original, using a digital processing technique.
2. Description of the Related Art
In an image forming device, a copying machine form an image of an original by thermal transfer, by use of a digital technique. These devices form an image on a sheet of paper whose size is the same as the image of the original. Enlarging or reducing the image of the original and forming such an image on the sheet of paper is sometimes called for.
In this type of copying machine, there are variations of magnification error in individual machines. For example, even if magnification of an image, which is projected on a photoelectric converting element array such as a CCD (charge coupled device) via an optical system, is set to 1.0, distortion due to errors of the optical system, that is, errors of magnification arise. Since such an error of magnification directly influences the image to be formed, it is required that the error of magnification be corrected with high accuracy.
In this adjustment, a difference between an image having an error magnification and an image having no error of magnification is measured by a jig, such as a scale, or by a operator's vision. Then, in order to remove the difference, physical or electrical correction is performed.
Therefore, in the above conventional adjustment of the optical system, since the image is always formed on a sheet of paper and a manual operation is carried out based on the formed image, the following disadvantages occur.
(1) Since the image must be formed at least once, time for forming the image and expendable supplies are needed.
(2) Since the standard of adjustment is easily changed, depending on differences of individual operator's vision, adjustment cannot be uniformly performed and a new variation is further generated.
(3) Since the operation of the adjustment and the image forming for confirming the adjustment result must be repeated so as to perform the adjustment with high accuracy, the time necessary for the operation of adjustment increases.